The present invention relates to an intake passage device for an internal combustion engine.
A small agricultural machine such as a portable trimmer and a shoulder spray may be used in an inclined position. In such a machine, it is necessary that the internal combustion engine mounted on the machine operates normally even if the machine is tilted.
In general, the internal combustion engine is manufactured by molding of aluminum alloy, so that the intake passage of the engine is tapered toward the intake port of the cylinder because of the draft of the mold. As a result, the speed of the mixture flowing from the carburetor to the intake port is reduced, which may cause particles of the fuel in the mixture to drop and stick on the inside wall of the intake passage.
Japanese Utility Model Publication 3-2698 discloses a device for removing the above described problem. In the device, a connecting pipe having a constant inside passage is connected between the carburetor and the intake port, thereby forming an intake passage having a constant inner diameter over the entire length of the passage. The inner end of the connecting pipe is engaged with an inside wall of a cylindrical projection of the intake port.
However, the inside wall of the cylindrical projection has a rough surface because of the molding without grinding. Therefore, liquefied fuel is liable to enter the space between the outer wall of the connecting pipe and the rough surface and to be accumulated therein. If the accumulated fuel discharges from the space due to the position of the engine and enters the combustion chamber of the engine, the combustion condition in the chamber may be affected to discharge incomplete combustion gases, causing air pollution.